Method for producing iron phosphate, method for producing lithium iron phosphate

Abstract

The present invention provides a method for producing iron phosphate and a method for producing lithium iron phosphate. The method for producing iron phosphate includes the steps of: uniformly mixing sulfate slag and sulfite with water to obtain a first mixture; adding phosphoric acid and a buffer to the first mixture to perform a leaching reaction; performing a first solid-liquid separation on the slurry obtained after the leaching reaction to obtain a first filtrate and a first filter cake; introducing air into the first filtrate to perform a first stirring reaction; performing a second solid-liquid separation on the slurry obtained after the first stirring reaction to obtain a second filtrate and a second filter cake; and calcining the second filter cake, the pressure of the leaching reaction is 0.25-0.5 MPa, the time is 1-2 hours, the pH of the reaction system of the leaching reaction is 1.5-3, and the buffer includes sodium dihydrogen phosphate and / or disodium hydrogen phosphate. The method for producing iron phosphate utilizes an iron source in sulfate slag, which can reduce the production cost of iron phosphate and is simple and easy to operate.

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application with application number 202210328818.0 and invention title "Method for Producing Iron Phosphate, Method for Producing Lithium Iron Phosphate", which was filed with the China National Intellectual Property Administration on March 30, 2022, and all of its content is incorporated herein by reference.

[0002] The present invention belongs to the technical field of batteries, and particularly relates to a method for producing iron phosphate and a method for producing lithium iron phosphate.

Background Art

[0003] Sulfate slag has a history of more than 100 years as a raw material for ironmaking and other purposes. The amount of sulfate slag discharged every year can reach more than 3 million tons, but only 1 million tons of it can be reasonably utilized, and the rest is discharged into the environment. When it accumulates, it occupies agricultural land and pollutes the land. When discharged into rivers or streams, it pollutes the water.

[0004] At present, there are many ways to comprehensively utilize sulfate slag, and most sulfate slag uses the method of "separating iron concentrate and manufacturing bricks from slag". As a raw material for ironmaking, separating iron concentrate from sulfate slag with an iron grade of 25% or more has certain economic value. The separation process is not very different from the general iron ore separation process. According to the high or low specific magnetization coefficient of iron minerals in the slag, gravity separation or magnetic separation methods can be used respectively. The economic analysis is as follows. If the annual separation amount of sulfate slag is 20,000 tons, when separating iron concentrate with an iron grade of 60 from slag with an iron grade of 30 (iron concentrate with an iron grade ≥ 60% can be directly used for ironmaking) and the yield is 40%, 8,000 tons of iron concentrate can be produced annually. Iron concentrate with an iron grade of 60 (sulfur content ≤ 0.5) has a price of 110 yuan per ton, a production cost of 70 yuan, and a profit of 40 yuan, and the annual profit is 320,000 yuan. The total investment in an iron separation plant is about 500,000 yuan, and all investments can be recovered within less than two years after production starts. After separating the iron concentrate, 12,000 tons of slag remain and can be used for brick manufacturing. Sulfate slag itself has no adhesive ability but contains active substances such as SiO2 and AI2O3.

[0005] Sulfate slag can be used as a raw material for sintered ore, mainly utilizing the iron-containing components in it to reduce the production cost of sintering raw materials. However, due to its low spheroidization property and high water absorption rate, it affects the sintering productivity. In addition, due to its high sulfur content and the presence of harmful elements such as Cu, Pb, and Zn, it affects the quality of sintered ore. The addition amount of sulfate slag in the sintering material is generally 10% or less. By processing sulfate slag to increase its fineness, improve its iron content, and reduce its sulfur content, it can be used as a raw material for ore pellets. In some prior technologies, a high-temperature chlorination process is used to chlorinate the metals contained in the slag, and then precious metals such as gold and silver are leached by hydrometallurgy to remove harmful metals in the slag.

[0006] With the development of lithium iron phosphate, inexpensive iron sources have attracted attention. Ferrous sulfate crystals, a by-product of titanium dioxide, have seen their prices continuously rise. Currently, the price has reached 350 yuan / ton, and the freight is approximately 70 - 90 yuan / ton. Moreover, with the expansion of the production capacity of lithium iron, the price of ferrous sulfate crystals has been rising steadily and it has become difficult to purchase. Therefore, the development of a new, inexpensive and easily obtainable iron source has become an urgent task. The annual production volume of sulfate slag is extremely large, reaching several million tons, and its recycling utilization rate is low.

[0007] In view of this, the present invention is proposed.

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of this, the object of the present invention is to provide a method for manufacturing iron phosphate and a method for manufacturing lithium iron phosphate. The method for manufacturing iron phosphate is simple and low-cost, and can recover cobalt, copper, gold, silver, sodium sulfate, etc. in sulfate slag, greatly improving the added value of sulfate slag and the resource utilization rate of sulfate slag.

Means for Solving the Problems

[0009] The present invention includes a step of uniformly mixing sulfate slag and sulfite with water to obtain a first mixed system; a step of adding phosphoric acid and a buffer to the first mixed system to carry out a leaching reaction; a step of performing a first solid-liquid separation on the slurry obtained after the leaching reaction to obtain a first filtrate and a first filter residue; a step of introducing air into the first filtrate to carry out a first stirring reaction; a step of performing a second solid-liquid separation on the slurry obtained after the first stirring reaction to obtain a second filtrate and a second filter residue; and a step of firing the second filter residue to obtain iron phosphate. the pressure of the leaching reaction is 0.25 - 0.5 MPa, and the time of the leaching reaction is 1 - 2 hours, the pH of the reaction system of the leaching reaction is 1.5 - 3, The present invention provides a method for producing iron phosphate, wherein the buffer contains sodium dihydrogen phosphate and / or disodium hydrogen phosphate.

[0010] Preferably, the particle size of the sulfate slag is 80-120 mesh. Preferably, the molar ratio of iron element in the sulfate slag, the sulfite, the phosphoric acid, and the buffer is 1:(0.35-0.4):(0.25-0.3):(1.7-1.75). Preferably, the phosphoric acid and the buffer are added to the first mixing system within 15-30 minutes. Preferably, the ratio of the amount of air introduced into the first filtrate per hour to the ferrous ions in the first filtrate is (8-12)m 3 :(28-32) mol.

[0011] The temperature of the leaching reaction is 130-170 °C. Preferably, the leaching reaction is carried out under stirring conditions.

[0012] Before introducing air into the first filtrate, the first filtrate is heated to 40-60 °C under stirring conditions. Preferably, the first stirring reaction specifically includes: stirring the first filtrate after introducing air until the content of iron element in the supernatant is 0.5 g / L or less, heating the first filtrate to 90-95 °C, and then stirring for another 30-60 minutes.

[0013] Before firing the second filter residue, it further includes washing and drying. Preferably, the temperature of the washing water for washing is 40-50 °C. Preferably, the washing is carried out until the pH of the washing liquid is 4.5 or higher. Preferably, the water content of the second filter residue after drying is 0.5% or less.

[0014] The firing temperature of the second filter residue is 650-680 °C. Preferably, the time for firing the second filter residue is 60 to 90 minutes.

[0015] The method for producing iron phosphate includes After the leaching reaction is completed, the method further includes the step of introducing the gas generated in the leaching reaction into a sodium hydroxide solution to obtain sodium sulfite.

[0016] The method for producing iron phosphate includes The method further includes the steps of cooling the second filtrate to perform a third solid-liquid separation to obtain sodium sulfate crystals and mother liquor, adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filter residue, adjusting the pH of the third filtrate to 9 to 10 to perform a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filter residue, firing the third filter residue, dissolving the fired third filter residue with sulfuric acid to obtain a second mixed system, and performing extraction, concentration, and crystallization on the second mixed system to obtain crude copper sulfate and crude cobalt sulfate. Preferably, the temperature after cooling the second filtrate is 5 to 10 °C, Preferably, the temperature for firing the third filter residue is 500 to 700 °C, Preferably, the time for firing the third filter residue is 2 to 4 hours.

[0017] The method for producing iron phosphate includes The method further includes the steps of adding aqua regia to the first filter residue concentrated by flotation to obtain a third mixed system, performing a fifth solid-liquid separation on the third mixed system to obtain a fifth filtrate, adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate, and adding iron powder to the sixth filtrate to obtain crude gold powder.

[0018] The present invention provides a method for producing lithium iron phosphate including the above method for producing iron phosphate.

[0019] The method for producing lithium iron phosphate is simple and low in cost.

Effect of the Invention

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows. (1) The method for producing iron phosphate according to the present invention skillfully utilizes high-pressure reduction leaching to dissolve iron trioxide and red iron oxide that are difficult to dissolve in acid, and at the same time uses a mixed solution of phosphoric acid and sodium dihydrogen phosphate to leach the reduced iron salt to obtain a ferrous dihydrogen phosphate solution. At the same time, at a high pH, it is possible to avoid the dissolution of some aluminum, calcium, magnesium, etc., greatly improving the leaching rate of iron, and using the leached iron for the production of iron phosphate. (2) The method for producing iron phosphate according to the present invention can also recover cobalt, copper, gold, silver, sodium sulfate, etc. in the sulfate slag, greatly improving the added value of the sulfate slag and the resource utilization rate of the sulfate slag. (3) The method for producing lithium iron phosphate according to the present invention is simple and low-cost.

Brief Description of the Drawings

[0021] Hereinafter, in order to more clearly explain the specific embodiments of the present invention or the technical solutions in the prior art, the drawings necessary for the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative labor.

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0022] The technical means of the present invention will be clearly and completely described below with reference to the drawings and specific embodiments. However, those skilled in the art should understand that the following-described embodiments are only some embodiments of the present invention, not all embodiments, and are merely for explaining the present invention and do not limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor shall fall within the protection scope of the present invention. For those not specified in the embodiments, the normal conditions or the conditions proposed by the manufacturer shall be followed. Those for which the manufacturer of the reagents or equipment used is not specified are all ordinary products that can be obtained from the market.

[0023] One aspect of the present invention is a step of uniformly mixing sulfate slag and sulfite with water to obtain a first mixed system, a step of adding phosphoric acid and a buffer to the first mixed system to perform a leaching reaction, a step of performing a first solid-liquid separation on the slurry obtained after the leaching reaction to obtain a first filtrate and a first filter residue, a step of introducing air into the first filtrate to perform a first stirring reaction, a step of performing a second solid-liquid separation on the slurry obtained after the first stirring reaction to obtain a second filtrate and a second filter residue, and a step of firing the second filter residue, wherein the pressure of the leaching reaction is 0.25 to 0.5 MPa, the pH of the reaction system of the leaching reaction is 1.5 to 3, and the buffer contains sodium dihydrogen phosphate and / or disodium hydrogen phosphate, and relates to a method for producing iron phosphate.

[0024] In some specific embodiments, the pressure of the leaching reaction may be, for example, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa or 0.5 MPa, but is not limited thereto.

[0025] In some specific embodiments, the pH of the reaction system of the leaching reaction may be, for example, 1.5, 2, 2.5 or 3, but is not limited thereto.

[0026] Sulfate slag is the slag produced by the process of manufacturing sulfuric acid from pyrite, also known as pyrite slag or calcined cinder, and is a type of chemical waste. Since the slag contains iron, it can be used as a raw material for steel metallurgy. The content of iron-containing oxides (Fe2O3, Fe3O4, FeO) in sulfate slag is about 20 - 50%, the silica content is about 15 - 65%, the alumina content is about 10%, the calcium oxide content is about 5%, the magnesium oxide content is 5% or less, the sulfur content is about 1 - 2%, and usually further contains copper, cobalt, lead, zinc, gold and silver. Magnetite forms dense magnetite due to the passivation effect of sulfuric acid.

[0027] The method for producing iron phosphate according to the present invention skillfully utilizes high-pressure reduction leaching to dissolve magnetite and red iron oxide that are difficult to dissolve in acid, and at the same time uses a mixed solution of phosphoric acid and sodium dihydrogen phosphate to leach the reduced iron salt to obtain a ferrous dihydrogen phosphate solution. At the same time, by controlling the pH of the reaction system of the leaching reaction to 1.5 - 3, it is possible to avoid the dissolution of some aluminum, calcium, magnesium, etc., and improve the leaching rate of iron.

[0028] Phosphoric acid can supply hydrogen ions. At the same time, sodium dihydrogen phosphate and disodium hydrogen phosphate are buffer solutions. After the hydrogen ions of phosphate ions are consumed, they can replenish hydrogen ions and avoid the leaching of other impurities due to the too low pH of the solution.

[0029] The leaching reaction of the present invention is carried out under specific leaching conditions, which greatly improves the leaching rate. By adding sulfite, it shows reducibility in an acidic environment, reduces ferric ions to ferrous ions, further improves the leaching rate, and finally ferrous dihydrogen phosphate can be obtained. At the same time, in an environment with a weak acidic environment and a large amount of dihydrogen phosphate ions, a ferrous dihydrogen phosphate solution is generated.

[0030] Preferably, the sulfite contains sodium sulfite and / or potassium sulfite.

[0031] Preferably, the particle size of the sulfate slag is 80 - 120 mesh.

[0032] In some specific embodiments, the particle size of the sulfate slag may be, for example, 80 mesh, 90 mesh, 100 mesh, 110 mesh or 120 mesh, but is not limited thereto.

[0033] Preferably, the molar ratio of the iron element in the sulfate slag, the sulfite, the phosphoric acid, and the buffer is 1:(0.35 - 0.4):(0.25 - 0.3):(1.7 - 1.75).

[0034] In some specific embodiments, the molar ratio of the iron element in the sulfate slag, the sulfite, the phosphoric acid, and the buffer may be, for example, 1:0.35:0.25:1.7, 1:0.37:0.28:1.173 or 1:0.4:0.3:1.75, but is not limited thereto.

[0035] Preferably, the phosphoric acid and the buffer are added to the first mixing system within 15 - 30 min (for example, 15 min, 20 min, 25 min or 30 min).

[0036] Preferably, the ratio of the amount of air introduced into the first filtrate per hour to the ferrous ions in the first filtrate is (8 - 12)m 3 :(28 - 32) mol.

[0037] In some specific embodiments, the ratio of the amount of air introduced into the first filtrate per hour to the ferrous ions in the first filtrate may be, for example, 8:28, 10:30 or 12:32, but is not limited thereto.

[0038] Preferably, the temperature of the leaching reaction is 130 - 170 °C.

[0039] In some specific embodiments, the temperature of the leaching reaction may be, for example, 130°C, 140°C, 150°C, 160°C, or 170°C, but is not limited thereto.

[0040] Preferably, the time of the leaching reaction is 1 to 2 hours.

[0041] In some specific embodiments, the time of the leaching reaction may be, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2 hours, but is not limited thereto.

[0042] Preferably, the leaching reaction is carried out under stirring conditions.

[0043] Preferably, before introducing air into the first filtrate, the first filtrate is heated to 40 - 60°C (for example, 40°C, 45°C, 50°C, 55°C, or 60°C) under stirring conditions.

[0044] Preferably, the first stirring reaction specifically includes stirring the first filtrate after introducing air until the content of iron element in the supernatant liquid is 0.5 g / L or less, heating the first filtrate to 90 - 95°C (for example, 90°C, 91°C, 92°C, 93°C, 94°C, or 95°C), and then stirring for another 30 - 60 min (for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min).

[0045] Preferably, before firing the second filter residue, it further includes washing and drying.

[0046] Preferably, the temperature of the washing is 40 - 50°C (for example, 40°C, 42°C, 44°C, 46°C, 48°C, or 50°C).

[0047] Preferably, washing is carried out until the pH of the washing liquid reaches 4.5 or more (for example, 4.5, 4.8, 5, 5.5, 6, or 6.5).

[0048] Preferably, the water content of the second filter residue after drying is 0.5% or less (for example, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%).

[0049] Preferably, the temperature for firing the second filter residue is 650 - 680°C (for example, 650°C, 655°C, 660°C, 665°C, 670°C, 675°C or 680°C).

[0050] Preferably, the time for firing the second filter residue is 60 - 90 min (for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min).

[0051] Preferably, after firing the second filter residue, cooling, pulverizing, sieving, iron removal and vacuum packaging are carried out to obtain anhydrous iron phosphate.

[0052] Preferably, the method for producing iron phosphate further includes a step of introducing the gas generated in the leaching reaction into a sodium hydroxide solution to obtain sodium sulfite for later use after the leaching reaction is completed.

[0053] Preferably, the method for producing iron phosphate further includes the steps of cooling the second filtrate to perform a third solid-liquid separation to obtain sodium sulfate crystals and mother liquor; adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filter residue; adjusting the pH of the third filtrate to 9 - 10 and performing a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filter residue; firing the third filter residue and dissolving the fired third filter residue in sulfuric acid to obtain a second mixed system; and performing extraction, concentration and crystallization on the second mixed system to obtain crude copper sulfate and crude cobalt sulfate.

[0054] Preferably, the temperature after cooling the second filtrate is 5 - 10°C (for example, 5°C, 7°C, 8°C, 9°C or 10°C).

[0055] After mixing sulfite into the second filtrate, sodium dihydrogen phosphate is mixed to convert it back to leach sulfate slag. The second filtrate is recycled three times and concentrated until the Baumé degree reaches 45 - 50, then cooled until the temperature of the second filtrate reaches 5 - 10 °C, centrifuged and dried, and the resulting crystals are sodium sulfate crystals.

[0056] After adding phosphoric acid and sodium dihydrogen phosphate to the fourth filtrate, it is converted back to leach sulfate slag.

[0057] Preferably, the temperature for firing the third filter residue is 500 - 700 °C (for example, 530 °C, 560 °C, 590 °C, 620 °C, 650 °C, 680 °C or 700 °C).

[0058] Preferably, the time for firing the third filter residue is 2 - 4 hours (for example, 2 h, 2.5 hours, 3 hours, 3.5 hours or 4 hours).

[0059] The waste gas generated by firing the third filter residue is absorbed with a sodium hydroxide solution and converted back to leach sulfate slag.

[0060] Preferably, the method for producing iron phosphate includes the steps of adding aqua regia to the first filter residue concentrated by flotation to obtain a third mixing system, performing a fifth solid-liquid separation on the third mixing system to obtain a fifth filtrate, adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate, and adding iron powder to the sixth filtrate to obtain crude gold powder.

[0061] The present invention uses the iron source in sulfate slag to produce iron phosphate, concentrates copper and cobalt in sulfate slag into crude copper sulfate and crude cobalt sulfate, and can also concentrate silver and gold in sulfate slag.

[0062] Another aspect of the present invention relates to a method for producing lithium iron phosphate further including the method for producing iron phosphate described above.

[0063] The manufacturing method of lithium iron phosphate is as follows.

[0064] Add a lithium source, a carbon source, and a dopant to the above anhydrous iron phosphate, add pure water, form a slurry, then perform nano-grinding, spray drying, bake the obtained spray-dried material in an inert atmosphere, and grind, screen, remove iron, and vacuum package the obtained baked material to obtain lithium iron phosphate.

[0065] The mass ratio of the anhydrous iron phosphate, the lithium source, the carbon source, and the dopant is 1:(0.2 - 0.25):(0.1 - 0.2):(0.0005 - 0.005). The lithium source is lithium carbonate or lithium hydroxide. The carbon source is at least one of glucose, sucrose, soluble starch, PEG, citric acid, ascorbic acid, and benzoic acid. The dopant is at least one of a titanium compound, a vanadium compound, a magnesium compound, and a manganese compound.

[0066] In the case of nano-grinding, grind until the particle size of the slurry reaches 100 - 600 nm. The inert atmosphere is nitrogen gas, the baking temperature is 600 - 900 °C, and the baking time is 5 - 40 hours.

[0067] The manufacturing method of the lithium iron phosphate is simple and low in cost.

Example

[0068] Hereinafter, in order to further illustrate the present invention, the manufacturing method of iron phosphate and the manufacturing method of lithium iron phosphate according to the present invention will be described in detail with reference to examples, but they cannot be understood as limitations on the protection scope of the present invention.

[0069] Example 1 The manufacturing method of iron phosphate according to this example includes the following steps (1) to (7).

[0070] In step (1), after pulverizing the sulfate slag with a ball mill, it is sieved through a 100-mesh sieve, and the detection data sampled from the sulfate slag are shown in Table 1.

[0071] Table 1 Specific information of sulfate slag

Table 1

[0072] In step (2), the sulfate slag is added into an autoclave, sodium sulfite solution is added, mixed and stirred, and a mixed solution of phosphoric acid and sodium dihydrogen phosphate is added into the autoclave by a high-pressure pump. While adding, the temperature is raised to 150 °C, the pressure in the autoclave is set to 0.42 MPa, the addition time of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is set to 20 min, and it is stirred and reacted at this temperature and pressure for 1.5 hours. The slurry after the reaction is filtered to obtain a first filtrate and a first filter residue. The first filter residue is sampled, and the detection data are shown in Table 2.

[0073] Table 2 Specific information of the first filter residue in Example 1

Table 2

[0074] The leaching rate of iron is higher than 95%, and elements such as gold and silver are concentrated.

[0075] In step (3), the temperature of the first filtrate is raised to 50 °C with stirring, then air is introduced, and the reaction is carried out with stirring under this condition until the concentration of iron element in the supernatant reaches 0.35 g / L. Then the temperature is raised to 95 °C, and the reaction is carried out with stirring at this temperature for 40 min. After filtration, the second filtrate and the second filter residue are obtained. After washing the second filter residue, it is dried and calcined in a rotary kiln. The calcination temperature is 670 °C and the calcination time is 80 min. The calcined material is cooled, pulverized, sieved, de-ironed and vacuum-packed to obtain anhydrous iron phosphate. The detection data of anhydrous iron phosphate are shown in Table 3. The results of observing iron phosphate with a scanning electron microscope are shown in Figures 1 and 2, and the particle size distribution of iron phosphate is shown in Figure 3.

[0076] Table 3 Detailed information of anhydrous iron phosphate

Table 3

[0077] In step (4), the second filtrate is returned to be mixed with sodium dihydrogen phosphate, and then returned to leach sulfate slag. Then, the second filtrate is recycled three times and concentrated until the Baumé degree reaches 48, and then cooled until the temperature of the solution reaches 8 °C, followed by centrifugation and drying. The obtained crystal is sodium sulfate crystal. Sodium sulfide solution is added to the mother liquor after crystallization, and after filtration, the third filtrate and the third filter residue are obtained. Then, sodium hydroxide is added to the third filtrate to adjust the pH of the solution to 9.5, and after filtration, the fourth filtrate and the fourth filter residue are obtained. The fourth filtrate is returned to be used in combination with a new phosphoric acid solution and sodium dihydrogen phosphate to obtain sodium sulfate crystals with a purity of 98.5% or more.

[0078] The molar ratio of iron element in sulfate slag, sodium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.37:0.3:1.7. The concentration of sodium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0079] In step (5), the third filter residue is calcined in a rotary kiln, the calcination temperature is 600 °C, the calcination time is 3 hours, the waste gas generated by the calcination is absorbed by a sodium hydroxide solution, and it is returned to leach out sulfate slag. After the third filter residue is calcined, sulfuric acid is added and dissolved. P204 extractant Cobalt and copper are extracted and separated by P204 extractant to obtain a cobalt-copper solution, which is then concentrated and crystallized to obtain crude copper sulfate with a purity of 95.6% and crude cobalt sulfate with a purity of 91.5%.

[0080] In step (6), after the first filter residue is subjected to flotation, gold and silver are further concentrated, aqua regia is added and dissolved, filtered, sodium chloride is added to the obtained filtrate to precipitate silver therein to obtain silver chloride, and iron powder is added to the remaining filtrate to displace gold therein to obtain crude gold powder.

[0081] In step (7), the gas in the autoclave is introduced into a 2 mol / L sodium hydroxide solution, and nitrogen gas is introduced into the autoclave. As a result, all sulfur dioxide gas is discharged and absorbed by the sodium hydroxide solution, and finally the sodium hydroxide concentration of the absorption solution becomes less than 0.2 mol / L. The obtained absorption solution is sodium sulfite, which is returned for reuse. The ratio of the flow rate (m 3 ) of the air introduced per hour to the total number of moles (mol) of ferrous ions in the solution is 20.

[0082] The method for manufacturing lithium iron phosphate is as follows.

[0083] A lithium source, a carbon source, and a dopant are added to the above anhydrous iron phosphate, pure water is added, after slurrying, it is nano-ground, spray-dried, the obtained spray-dried material is calcined in an inert atmosphere, and the obtained calcined material is ground, sieved, de-ironed, and vacuum-packed to obtain lithium iron phosphate.

[0084] The mass ratio of anhydrous iron phosphate, lithium source, carbon source, and dopant was 1:0.23:0.13:0.0015. The lithium source was lithium carbonate, the carbon source was glucose, and the dopant was titanium dioxide.

[0085] In the case of nano-grinding, it was ground until the particle size of the slurry reached 320 nm. The inert atmosphere was nitrogen gas, the firing temperature was 780 °C, and the firing time was 12 hours.

[0086] The detection data of the final lithium iron phosphate are as follows.

Table 4

[0087] The powder resistivity was measured by the four-probe method, and the pressure was 10 MPa.

[0088] The pressure used to obtain the press density was 3 T.

[0089] Example 2 The method for manufacturing iron phosphate according to this example includes the following steps (1) to (7).

[0090] Step (1) is the same as in Example 1.

[0091] In step (2), sulfate slag was added into the autoclave, potassium sulfite solution was added, mixed and stirred, and a mixed solution of phosphoric acid and sodium dihydrogen phosphate was added into the autoclave by a high-pressure pump while heating up to 130 °C. The pressure in the autoclave was set to 0.5 MPa, the addition time of the mixed solution of phosphoric acid and sodium dihydrogen phosphate was set to 15 min, and it was stirred and reacted at this temperature and pressure for 2 hours. The slurry after the reaction was filtered to obtain the first filtrate and the first filter residue.

[0092] In step (3), the temperature of the first filtrate is raised to 40 °C with stirring, then air is introduced, and the reaction is carried out under this condition with stirring until the concentration of iron element in the supernatant reaches 0.1 g / L. Then the temperature is raised to 95 °C, and the reaction is carried out with stirring at this temperature for 30 min. After filtration, the second filtrate and the second filter residue are obtained. After washing the second filter residue, it is dried, calcined in a rotary kiln, the calcination temperature is 680 °C, and the calcination time is 60 min. Cooling, pulverizing, sieving, iron removal and vacuum packaging are carried out on the calcined material to obtain anhydrous iron phosphate.

[0093] In step (4), the second filtrate is returned to be mixed with sodium dihydrogen phosphate, and then returned to leach sulfate slag. Then, the second filtrate is recycled three times and concentrated until the Baume degree reaches 48, and then cooled until the temperature of the solution reaches 8 °C, followed by centrifugation and drying. The obtained crystals are sodium sulfate crystals. Sodium sulfide solution is added to the mother liquor after crystallization, and after filtration, the third filtrate and the third filter residue are obtained. Then, sodium hydroxide is added to the third filtrate to adjust the pH of the solution to 9, and after filtration, the fourth filtrate and the fourth filter residue are obtained. The fourth filtrate is returned to be used in combination with a new phosphoric acid solution and sodium dihydrogen phosphate.

[0094] The molar ratio of iron element in sulfate slag, potassium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.35:0.25:1.7. The concentration of potassium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0095] In step (5), the third filter residue is calcined in a rotary kiln, the calcination temperature is 500 °C, and the calcination time is 4 hours. The waste gas generated by calcination is absorbed with sodium hydroxide solution and returned to leach sulfate slag. After the third filter residue is calcined, sulfuric acid is added for dissolution, and cobalt and copper are extracted and separated with P204 extractant to obtain a cobalt-copper solution. Then, it is concentrated and crystallized to obtain crude copper sulfate and crude cobalt sulfate.

[0096] Steps (6) to (7) are the same as those in Example 1.

[0097] Example 3 The method for producing iron phosphate according to this example includes the following steps (1) to (7).

[0098] Step (1) is the same as that in Example 1.

[0099] In step (2), sulfate slag is added into an autoclave, sodium sulfite solution is added, mixed and stirred, and a mixed solution of phosphoric acid and sodium dihydrogen phosphate is added into the autoclave by a high-pressure pump while heating up to 170 °C. The pressure in the autoclave is set to 0.25 MPa, the addition time of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is set to 30 min, and the reaction is carried out by stirring for 1 hour at this temperature and pressure. The slurry after the reaction is filtered to obtain a first filtrate and a first filter residue.

[0100] In step (3), the first filtrate is heated up to 60 °C with stirring, then air is introduced, and the reaction is carried out by stirring under this condition until the concentration of iron element in the supernatant reaches 0.5 g / L. Then it is heated up to 90 °C and stirred at this temperature for 60 min for reaction, filtered to obtain a second filtrate and a second filter residue. After washing the second filter residue, it is dried, calcined in a rotary kiln, the calcination temperature is 650 °C, the calcination time is 90 min, and the calcined material is cooled, pulverized, sieved, de-ironed and vacuum-packed to obtain anhydrous iron phosphate.

[0101] In step (4), the second filtrate is returned to be mixed with sodium dihydrogen phosphate, and then returned to leach sulfate slag. Then, the second filtrate is recycled three times and concentrated until the Baume degree reaches 48, and then cooled until the temperature of the solution reaches 8°C, centrifuged and dried. The obtained crystals are sodium sulfate crystals. A sodium sulfide solution is added to the mother liquor after crystallization, filtered to obtain a third filtrate and a third filter residue. Then, sodium hydroxide is added to the third filtrate to adjust the pH of the solution to 10, filtered to obtain a fourth filtrate and a fourth filter residue, and the fourth filtrate is returned to be used in combination with a new phosphoric acid solution and sodium dihydrogen phosphate.

[0102] The molar ratio of iron element in sulfate slag, sodium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.4:0.3:1.75. The concentration of the sodium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0103] In step (5), the third filter residue is calcined in a rotary kiln. The calcination temperature is 700°C, and the calcination time is 2 hours. The waste gas generated by calcination is absorbed with a sodium hydroxide solution and returned to leach sulfate slag. After the third filter residue is calcined, sulfuric acid is added and dissolved, and cobalt and copper are extracted and separated with a P204 extractant to obtain a cobalt-copper solution, and then concentrated and crystallized to obtain crude copper sulfate and crude cobalt sulfate.

[0104] Steps (6)-(7) are the same as in Example 1.

[0105] Comparative Example 1 The method for producing iron phosphate according to this comparative example is different from Example 1 only in that the pressure of the leaching reaction is 0.1 MPa and the leaching rate of iron is 83%.

[0106] Comparative Example 2 The method for producing iron phosphate according to this comparative example is different from Example 1 only in that the pH of the reaction system of the leaching reaction is 1. The detailed information of the obtained first filter residue is shown in Table 4 respectively.

[0107] Table 4 Specific information of the first filter residue in Comparative Example 2

Table 5

[0108] Comparative Example 3 The method for producing iron phosphate according to this comparative example is different from Example 1 only in that the time of the leaching reaction is 0.5 hours and the leaching rate of iron is 81%.

[0109] By comparing Example 1, Comparative Example 1 and Comparative Example 3, it can be seen that if the pressure and time of the leaching reaction are not within a certain range, the leaching effect of iron cannot be guaranteed.

[0110] By comparing Example 1 and Comparative Example 2, it can be seen that when the pH is low, the leaching rate of other impurities is greatly improved, a large amount of impurities are introduced into the iron-containing solution, which affects the leaching effect of iron, and if the pH is not within a certain range, the leaching purity of iron cannot be guaranteed.

[0111] The present invention has been described and illustrated with reference to specific embodiments. However, each of the above embodiments is only for explaining the technical means of the present invention and is not a limiting one. Those skilled in the art should understand that without departing from the spirit and scope of the present invention, the technical means described in each of the above embodiments can be modified, or equivalent substitutions can be made for some or all of the technical features thereof. These modifications and substitutions do not depart from the essence of the corresponding technical means from the scope of the technical means of each embodiment of the present invention. Therefore, it is meant that the appended claims cover all alternatives and modifications that fall within the protection scope of the present invention.

[0112] The above description is only a preferred embodiment of the present invention. For those skilled in the art, various improvements and modifications can be made on the premise of not departing from the principles described in the present invention, and these improvements and modifications should also be regarded as within the protection scope of the present invention.

Claims

1. obtaining a first mixed system by uniformly mixing sulfate slag and sulfite with water; performing a leaching reaction by adding phosphoric acid and a buffer to the first mixed system; performing a first solid-liquid separation on the slurry obtained after the leaching reaction to obtain a first filtrate and a first filter residue; introducing air into the first filtrate to perform a first stirring reaction; performing a second solid-liquid separation on the slurry obtained after the first stirring reaction to obtain a second filtrate and a second filter residue; firing the second filter residue to obtain iron phosphate, comprising: the pressure of the leaching reaction is 0.25 to 0.5 MPa; the time of the leaching reaction is 1 to 2 hours; the pH of the reaction system of the leaching reaction is 1.5 to 3; the buffer contains sodium dihydrogen phosphate and / or disodium hydrogen phosphate, a method for producing iron phosphate.

2. the particle size of the sulfate slag is 80 to 120 mesh; the molar ratio of iron element in the sulfate slag, the sulfite, the phosphoric acid, and the buffer is 1: (0.35 to 0.4): (0.25 to 0.3): (1.7 to 1.75); the phosphoric acid and the buffer are added to the first mixed system within 15 to 30 minutes; The ratio of the amount of air introduced into the first filtrate per hour to the ferrous ions in the first filtrate is (8 - 12) m ３ :(28 - 32) mol. The method for producing iron phosphate according to claim 1.

3. the temperature of the leaching reaction is 130 to 170 °C; the leaching reaction is performed under stirring conditions, the method for producing iron phosphate according to Claim 1.

4. before introducing air into the first filtrate, under stirring conditions, heating the first filtrate to 40 to 60 °C; the first stirring reaction specifically is: stirring the first filtrate after introducing air until the content of iron element in the supernatant liquid is 0.5 g / L or less, heating the first filtrate to 90 to 95 °C, and then stirring for another 30 to 60 minutes, the method for producing iron phosphate according to Claim 1.

5. before firing the second filter residue, further including washing and drying; the temperature of the washing water for washing is 40 to 50 °C; washing until the pH of the washing liquid is 4.5 or more; the water content of the second filter residue after drying is 0.5% or less, the method for producing iron phosphate according to Claim 1.

6. the temperature for firing the second filter residue is 650 to 680 °C; the time for firing the second filter residue is 60 to 90 minutes, the method for producing iron phosphate according to Claim 1.

7. The method for producing iron phosphate according to claim 1, further comprising the step of introducing the gas generated in the leaching reaction into a sodium hydroxide solution after the leaching reaction is completed to obtain sodium sulfite.

8. The step of cooling the second filtrate to perform a third solid-liquid separation to obtain sodium sulfate crystals and mother liquor; The step of adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filter residue; The step of adjusting the pH of the third filtrate to 9-10 and performing a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filter residue; The step of firing the third filter residue and dissolving the fired third filter residue in sulfuric acid to obtain a second mixed system; The method further comprising the steps of performing extraction, concentration, and crystallization on the second mixed system to obtain crude copper sulfate and crude cobalt sulfate; The temperature after cooling the second filtrate is 5-10 °C; The temperature for firing the third filter residue is 500-700 °C; The time for firing the third filter residue is 2-4 hours. The method for producing iron phosphate according to claim 1.

9. The step of adding aqua regia to the first filter residue concentrated by flotation to obtain a third mixed system; The step of performing a fifth solid-liquid separation on the third mixed system to obtain a fifth filtrate; The step of adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate; The method for producing iron phosphate according to claim 1, further comprising the step of adding iron powder to the sixth filtrate to obtain crude gold powder.

10. The method for producing lithium iron phosphate, comprising the method for producing iron phosphate according to any one of claims 1 to 9.

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